The present invention pertains to a device for producing collections of sheet-like printed products, as well as to a folding apparatus.
EP 0 257 390 A1 discloses a folding apparatus that produces multi-sheet folded collections of a supplied paper web. The folding apparatus comprises a first longitudinal folding device, by means of which the supplied web is centrally folded along its length and fed to a cross-cutting device. This cross-cutting device separates corresponding folded sections from the folded web. The cross-cutting device features a cutting cylinder that extends across the folded paper web and cooperates with a grooved cylinder. The cutting cylinder contains two knife receptacles that are offset relative to one another by 180° and can be selectively fitted with a knife. It is therefore possible to selectively produce two different cut-off lengths, which respectively correspond to the full circumference and half the circumference of the cutting cylinder, depending on the knife fitting.
A cross-folding device is arranged downstream of this cross-cutting device, wherein the collecting cylinder of said cross-folding device cooperates with at least one folding jaw cylinder. To this end, the collecting cylinder is equipped with two sets of grippers that are arranged on mutually adjustable armature carriers. The collecting cylinder receives the sections arriving from the cross-cutting device with these grippers and releases them to the folding cylinder. To this end, the grippers are actuated by means of a cam drive. The grippers of the collecting cylinder have to be respectively adjusted to the product thickness in order to process collections of different thickness. This leads to a significant set-up effort.
In order to eliminate this disadvantage, DE 101 56 706 A1 proposes a collecting cylinder that is equipped with holding elements in the form of puncture elements rather than grippers. The controllable puncture elements are formed by sets of needles. The needles protrude over the circumference of the collecting cylinder for transporting and collecting the products such that they can be pinned thereon. The puncture elements are retracted in order to fold and forward the products. In this case, the motion of the puncture elements is not dependent on the product thickness such that the variability of such a folding apparatus with respect to the product thickness is significantly improved.
Regardless of the holding system used, these folding apparatuses have the disadvantage that the section length is defined by the diameter and the knife fitting of the cutting cylinder. A change of the knife fitting is labor-intensive and requires a production downtime. A digital web-fed printing press equipped with such a folding apparatus is therefore restricted to a few formats with respect to the section length. The utilization of servomotors in fact makes it possible to eliminate the disadvantage of such a format restriction.
Due to the principle involved, a change from a continuous material transport, which is characterized by a constant web speed, to a cyclic transport of the separated sections with a constant cycle speed takes place. The production of highly different product lengths therefore requires such high dynamics of the different cylinder motions that they cannot be economically realized. An attempt to solve this problem by restricting the potential format range dramatically reduces the variability of the digital printing press.